1. Field of the Invention
The present invention is related to the expansion of the capacity of a Single Inline Memory Module (SIMM). Specifically, the present invention is a method that allows the expansion of the Memory Module and its addressing system without adding additional address and type pins to the existing SIMMs.
2. Description of the Related Art
In modern computer technology, advanced computer software and operating system functions necessitate additional memory space. The main memory space in a personal computer (PC) comprises multiple Dynamic Random Access Memory (DRAM) chips which in the past were physically socketed on the motherboard of the PC. A typical PC requires a minimum of 15-30 DRAMs in order to operate at its most basic level. In order to run more complex applications additional memory capacity is required, therefore additional DRAM chips must be installed.
It can be very time consuming to add or replace large numbers of DRAM chips, as each individual chip must be installed by hand. In addition, it is possible to orient the chips wrong during installation. Improper orientation could result in bending the chip leads, poor connection of the chip leads to the socket, or installing the chips backwards, all of which may render the DRAM chip intermittently or permanently inoperable. If one of the DRAM chips is inoperable, a portion of the computer system's memory will no longer be addressable. If a DRAM chip becomes inoperable during normal operation after installation, not only will the chip be unaddressable, but all the information stored on that chip will be lost. Thus, to decrease the possibility of improper memory installation during memory expansion, a more easily installable memory unit is required.
The DRAM chips occupy a large percentage of the motherboard and therefore limit the space available for circuitry. Space must be reserved on the motherboard to enable memory future expansion, and this limits the space available for adding other functions. As space is one of the most important elements of motherboard design, the required memory spacing weighs heavily on the overall system design. As the computer industry is constantly pushing for smaller and smaller computer systems, the development of a less space consuming memory system was necessitated.
The computer industry has mitigated the memory spacing problems to some degree, by creating the Single Inline Memory Module (SIMM) concept. A SIMM is a small circuit board with a predetermined group of DRAM chips soldered into the board. The SIMM circuit board can be easily installed in a specialized socket on the motherboard. The circuit board simply snaps into the socket without the need for specialized tools or procedures, and has only one allowable orientation in the socket. The circuit boards are installed in the sockets at an approximately perpendicular orientation to the motherboard, and therefore do not use as much space as the previous horizontal orientation of the individual DRAM chips. The SIMM concept has helped minimize the space and installation problems of the individually installable DRAM systems.
The industry has developed several different standard sizes of sockets, printed circuit cards and memory densities for the SIMMs. The one limiting factor of the SIMM design is the interconnection between the printed circuit cards and the motherboard through the sockets. In order to upgrade the memory capacity of an individual SIMM, not only are new address lines required, but new systems for indicating the capacity of the SIMMs to the motherboard must be implemented. As every upgrade necessitates more lines of communication between the SIMM and the motherboard, additional pins must be available on the printed circuit board and accompanying socket of the SIMM. Once all the pins on the printed circuit boards have been utilized, an entirely new board and accompanying mating socket must be designed to enable memory capacity upgrades. This is very costly to implement and would render all the older SIMM printed circuit boards and sockets inoperable, as they could not properly communicate with the each new SIMM support system.
Accordingly, memory system upgrades are limited by the inadequacies of the existing SIMM technology.